The present disclosure relates generally to acoustic measurements. In particular, the present disclosure relates to accurately measuring coherent noise and removing the coherent noise from pulse echo measurements.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as any limitation to the claimed subject matter.
A wellbore may be drilled into a geological formation to extract oil and/or gas from the geological formation. Logging tools may determine a variety of characteristics of the wellbore and/or the geological formation. Logging tools may determine characteristics of the surrounding rock formation. Logging tools may also determine whether cement injected around the wellbore properly achieves zonal isolation. That is, to prevent the certain zones of the geological formation from interacting with one another within the wellbore and to prevent fluids from undesired zones entering the wellbore, the wellbore may be constructed by inserting a cylindrical casing into the wellbore and injecting the cement injected into an annulus between the casing and a wall of the wellbore (i.e., the geological formation). When the cement properly sets, fluids from one zone of the geological formation may be prevented from passing through the wellbore to interact with one another. However, the cement may not set as planned and/or the quality of the cement may be less than expected. Additionally, the cement may unexpectedly fail to set above a certain depth due to natural fissures in the geological formation.
A variety of pulse echo tools may be used to verify that the cement is properly installed. These pulse echo tools may pulse and measure reflected acoustic (e.g., sonic or ultrasonic) waves through the wellbore to obtain acoustic cement evaluation data at various depths and azimuths in the wellbore. However, recent developments in drilling and constructing the wellbore may reduce the strength of an acoustic signal to be measured. For example, the wellbore is increasingly drilled using heavier drilling fluids and constructed using thicker casings, which may attenuate the acoustic signal more than lighter drilling fluids and thinner casings. In addition, well casings are increasingly being installed using lighter cements that have acoustic properties more similar to fluids than heavier cements. To account for these developments, the operating frequency of pulse echo tools may be reduced, but doing so may introduce noise due to pulse echo tool electronics and intrinsic noise of a transducer of the pulse echo tools. This may be the case when using the transducer for both excitation and measurement.